U.S. patent application number 13/058770 was filed with the patent office on 2011-06-16 for fuel cell system and electronic device.
This patent application is currently assigned to SONY CORPORATION. Invention is credited to Yoshiaki Inoue, Jusuke Shimura.
Application Number | 20110140547 13/058770 |
Document ID | / |
Family ID | 41707109 |
Filed Date | 2011-06-16 |
United States Patent
Application |
20110140547 |
Kind Code |
A1 |
Shimura; Jusuke ; et
al. |
June 16, 2011 |
FUEL CELL SYSTEM AND ELECTRONIC DEVICE
Abstract
A fuel cell system that is able to perform power generation more
stably than in the past regardless of external environment is
provided. Based on a temperature of a power generation section
detected by a temperature detection section, a supply amount of a
liquid fuel from a fuel pump is adjusted, and therefore control in
which the temperature of the power generation section becomes
constant is performed. In addition, a fuel cell system that is able
to perform power generation in a vaporization supply type fuel cell
more stably than in the past is provided. A level of a power
generation voltage supplied from the power generation section is
raised by a boost circuit. In a control section, operation of the
boost circuit is controlled using a given control table, and
therefore control is performed on an output voltage and an output
current supplied from the boost circuit to a load.
Inventors: |
Shimura; Jusuke; (Kanagawa,
JP) ; Inoue; Yoshiaki; (Aichi, JP) |
Assignee: |
SONY CORPORATION
Tokyo
JP
|
Family ID: |
41707109 |
Appl. No.: |
13/058770 |
Filed: |
July 29, 2009 |
PCT Filed: |
July 29, 2009 |
PCT NO: |
PCT/JP2009/063463 |
371 Date: |
February 11, 2011 |
Current U.S.
Class: |
307/151 ;
429/431; 429/432; 429/442 |
Current CPC
Class: |
Y02E 60/523 20130101;
H01M 8/04589 20130101; H01M 8/1011 20130101; H01M 8/04731 20130101;
H01M 8/04753 20130101; H01M 8/04365 20130101; Y02E 60/50 20130101;
H01M 8/04201 20130101; H01M 8/04559 20130101; H01M 8/0432
20130101 |
Class at
Publication: |
307/151 ;
429/442; 429/432; 429/431 |
International
Class: |
H01M 8/04 20060101
H01M008/04; G05F 1/46 20060101 G05F001/46 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 18, 2008 |
JP |
P2008-209873 |
Sep 11, 2008 |
JP |
P2008-233116 |
Claims
1-20. (canceled)
21. A fuel cell system comprising: a power generation section for
performing power generation by being supplied a fuel and oxidant
gas; a fuel supply section for supplying a liquid fuel to the power
generation section side and in which a supply amount of the liquid
fuel is able to be adjusted; a fuel vaporization section for
supplying a gas fuel to the power generation section by vaporizing
the liquid fuel supplied from the fuel supply section; a
temperature detection section for detecting temperature of the
power generation section; and a control section for performing
control so that the temperature of the power generation section
becomes constant by adjusting the supply amount of the liquid fuel
from the fuel supply section based on the temperature of the power
generation section detected by the temperature detection
section.
22. The fuel cell system according to claim 21, wherein the control
section calculates approximate energy conversion efficiency in the
power generation section based on a power generation voltage of the
power generation section or a given setting voltage, and corrects
the supply amount of the liquid fuel using the calculated energy
conversion efficiency.
23. The fuel cell system according to claim 22, wherein the control
section calculates the energy conversion efficiency in the power
generation section also taking into consideration a power
generation current of the power generation section, in addition to
the power generation voltage of the power generation section or the
given setting voltage.
24. The fuel cell system according to claim 21, comprising: a
current detection section for detecting a power generation current
of the power generation section, wherein the control section
calculates a usage rate of fuel in the power generation section
based on the power generation current detected by the current
detection section, and calculates the supply amount of the liquid
fuel so that the calculated usage rate of fuel becomes constant,
and determines a final supply amount of the liquid fuel taking into
consideration a first fuel supply amount calculated based on the
temperature of the power generation section and a second fuel
supply amount calculated based on the usage rate of fuel.
25. The fuel cell system according to claim 24, wherein the control
section determines the final supply amount of the liquid fuel by
selecting one of the first and second fuel supply amounts.
26. The fuel cell system according to claim 25, wherein the control
section determines the final supply amount of the liquid fuel by
selecting a smaller supply amount value of the first fuel supply
amount and the second fuel supply amount.
27. The fuel cell system according to claim 24, wherein the control
section periodically updates a setting value of the usage rate of
fuel.
28. The fuel cell system according to claim 21, wherein the control
section performs control so that the temperature of the power
generation section becomes constant by proportioning the supply
amount of the liquid fuel with a time integral and a time
derivative of a difference value between a setting temperature and
the detected temperature of the power generation section.
29. The fuel cell system according to claim 21, wherein the control
section performs control so that the temperature of the power
generation section becomes constant by proportioning the supply
amount of the liquid fuel with a difference value between a setting
temperature and the detected temperature of the power generation
section.
30. The fuel cell system according to claim 21, wherein the control
section performs control so that the temperature of the power
generation section becomes constant by proportioning the supply
amount of the liquid fuel with a time integral of a difference
value between a setting temperature and the detected temperature of
the power generation section.
31. The fuel cell system according to claim 21, wherein the control
section performs control so that the temperature of the power
generation section becomes constant by proportioning the supply
amount of the liquid fuel with a time derivative of a difference
value between a setting temperature and the detected temperature of
the power generation section.
32. An electronic device including a fuel cell system, the fuel
cell system comprising: a power generation section for performing
power generation by being supplied a fuel and oxidant gas; a fuel
supply section for supplying a liquid fuel to the power generation
section side and in which a supply amount of the liquid fuel is
able to be adjusted; a fuel vaporization section for supplying a
gas fuel to the power generation section by vaporizing the liquid
fuel supplied from the fuel supply section; a temperature detection
section for detecting temperature of the power generation section;
and a control section for performing control so that the
temperature of the power generation section becomes constant by
adjusting the supply amount of the liquid fuel by the fuel supply
section based on the temperature of the power generation section
detected by the temperature detection section.
33. A fuel cell system comprising: a power generation section for
performing power generation by being supplied a fuel and oxidant
gas; a fuel supply section for supplying a liquid fuel to the power
generation section side and in which a supply amount of the liquid
fuel is able to be adjusted; a fuel vaporization section for
supplying a gas fuel to the power generation section by vaporizing
the liquid fuel supplied from the fuel supply section; a boost
circuit for increasing a power generation voltage supplied from the
power generation section; and a control section for performing
control on a load voltage and a load current supplied from the
boost circuit to a load by controlling operation of the boost
circuit using a given control table.
34. The fuel cell system according to claim 33, wherein the control
section performs operation control of the boost circuit so that the
load voltage becomes constant.
35. The fuel cell system according to claim 34, wherein the boost
circuit performs a voltage raising operation according to a
potential comparison result of a voltage based on the load voltage
and a given reference voltage, and the control section performs
operation control of the boost circuit so that a setting value of
the reference voltage increases as a setting value of the load
voltage increases.
36. The fuel cell system according to claim 34, wherein the control
section performs operation control of the boost circuit using the
control table so that the load current becomes smaller as the
setting value of fuel conversion efficiency in the power generation
section increases.
37. The fuel cell system according to claim 33, wherein the control
section performs operation control of the boost circuit so that the
load current becomes constant.
38. The fuel cell system according to claim 33, wherein the control
section adjusts magnitudes of the load voltage and the load current
according to size of the load using the control table in a case
where the supply amount of the liquid fuel from the fuel supply
section is constant.
39. The fuel cell system according to claim 33, wherein the boost
circuit includes a DC/DC converter.
40. An electronic device including a fuel cell system, the fuel
cell system comprising: a power generation section for performing
power generation by being supplied a fuel and oxidant gas; a fuel
supply section for supplying a liquid fuel to the power generation
section side and in which a supply amount of the liquid fuel is
able to be adjusted; a fuel vaporization section for supplying a
gas fuel to the power generation section by vaporizing the liquid
fuel supplied from the fuel supply section; a boost circuit for
raising a power generation voltage level supplied from the power
generation section; and a control section for performing control on
a load voltage and a load current supplied from the boost circuit
to a load by controlling operation of the boost circuit using a
given control table.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a National Stage of International
Application No. PCT/JP2009/063463 filed on Jul. 29, 2009 and which
claims priority to Japanese Patent Application No. JP 2008-209873
filed on Aug. 18, 2008 and JP 2008-233116 filed on Sep. 11, 2008,
the entire contents of which are being incorporated herein by
reference.
BACKGROUND
[0002] Fuel cells have high power generation efficiency and do not
exhaust harmful matter, the fuel cells have been practically used
as an industrial power generation equipment and a household power
generation equipment, or as a power source for an artificial earth
satellite, a space ship or the like. Further, in recent years, the
fuel cells have been progressively developed as a power source for
a vehicle such as a passenger car, a bus, and a cargo truck. Such
fuel cells are categorized into an alkali aqueous solution fuel
cell, a phosphoric-acid fuel cell, a molten carbonate fuel cell, a
solid oxide fuel cell, a direct methanol fuel cell and the like.
Specially, a solid polyelectrolyte DMFC (Direct Methanol Fuel Cell)
is able to provide a high energy density by using methanol as a
fuel hydrogen source. Further, the DMFC does not need a reformer
and thus is able to be downsized. Thus, the DMFC as a small mobile
fuel cell has been progressively researched.
[0003] In the DMFC, an MEA (Membrane Electrode Assembly) as a unit
cell in which a solid polyelectrolyte film is sandwiched between
two electrodes, and the resultant is joined and integrated is used.
One gas diffusion electrode is used as a fuel electrode (anode),
and methanol as a fuel is supplied to the surface of such one gas
diffusion electrode. As a result, the methanol is decomposed,
hydrogen ions (protons) and electrons are generated, and the
hydrogen ions pass through the solid polyelectrolyte film. Further,
the other gas diffusion electrode is used as an oxygen electrode
(cathode), and air as oxidant gas is supplied to the surface of the
other gas diffusion electrode. As a result, oxygen in the air is
bonded with the foregoing hydrogen ions and the foregoing electrons
to generate water. Such electrochemical reaction results in
generation of electro motive force from the DMFC.
[0004] Meanwhile, in a fuel cell used for mobile purposes, it is
desired that the fuel cell stably perform power generation
operation in any environment, such as indoors, outdoors in
midwinter, inside an automobile at high midsummer temperatures, and
inside a bag where heat release is difficult. Further, it is also
desired that the fuel cell be able to follow sudden changes in the
environment, such as the fuel cell suddenly being carried from
inside a warm room to freezing outdoors. In this way, since
suitable fuel supply amount for the fuel cell differs according to
the temperature and humidity of the external environment, careful
fuel supply control according to environment changes (fuel supply
control in which the fuel supply amount is not excessive or
insufficient) is desired.
[0005] In a case where the supply amount of fuel becomes excessive,
the surplus fuel permeates to the oxygen electrode, thereby causing
a phenomenon called crossover. The crossover phenomenon is a
phenomenon in which the surplus fuel burns directly on the oxygen
electrode, thus not only reducing usage efficiency of fuel and
causing waste, but also carrying risk of causing burn injury to a
user resulting from temperature rise. In addition, on the contrary,
in a case where the fuel supply becomes insufficient, sufficient
output is not able to be obtained, and there is a possibility that
power supply to equipment connected to the fuel cell is
stopped.
[0006] Thus, a method of controlling the fuel supply amount for the
purpose of inhibiting excess and shortage in the fuel supply amount
has been proposed (for example, Patent Document 1).
[0007] In fuel cell systems including a fuel cell such as the
foregoing, there is a fuel cell system in which a power generation
voltage and a power generation current (generated power) from the
fuel cell charge a secondary battery and drive a load. Thereby, in
such a fuel cell system, it is desired that the generated power
from the fuel cell charges the secondary battery as efficiently as
possible.
[0008] In Patent Document 2, a fuel cell system in which control is
performed so that the power generation voltage value of the fuel
cell is held constant using a DC/DC converter is proposed.
[0009] Patent Document
[0010] Patent Document 1: Japanese Unexamined Patent Application
Publication No. 2007-227336
[0011] Patent Document 2: Japanese Unexamined Patent Application
Publication No. 2006-501798
SUMMARY
[0012] In the fuel supply control in the foregoing Patent Document
1, two threshold values (an upper limit value and a lower limit
value) are set for voltage and current. The fuel supply is stopped
when the upper limit value is exceeded, whereas the fuel supply is
resumed when the value falls below the lower limit value. According
to the control method, the fuel supply is able to be controlled by
voltage fluctuations during constant current power generation and
by current fluctuations during constant voltage power
generation.
[0013] However, in the control method, for example, there has been
a problem that, in the case where the crossover phenomenon occurs,
the situation is worsened. Specifically, for example, while the
voltage decreases and falls below the lower limit value when fuel
is insufficient during constant current control, since the voltage
similarly decreases when the crossover phenomenon occurs as well,
the voltage falls below the lower limit value. Here, in the former
(when fuel is insufficient), it is necessary to supply fuel, while
in the latter (when crossover phenomenon occurs), it is necessary
to stop fuel supply. However, since focus is placed merely on the
voltage in the fuel supply control of the past, there has been a
problem that the difference between the former and the latter is
not able to be differentiated.
[0014] In such a DMFC, as a method of supplying methanol to the
fuel electrode, a liquid supply type fuel cell (a liquid fuel
(methanol aqueous solution) is directly supplied to the fuel
electrode) and a vaporization supply type fuel cell (a vaporized
liquid fuel is supplied to the fuel electrode) are proposed. Of the
foregoing, in the vaporization supply type fuel cell, fuel supply
control according to the concentration of fuel such as in the
liquid supply type fuel cell is not able to be performed, and the
fuel supply control is performed according to a fuel supply cycle
(such as an operation timing of a fuel supply pump, or an
opening/closing timing of a shutter). Thereby, in the vaporization
supply type DMFC in particular, it is desired that a stable power
generation operation independent of the external environment be
actualized by inhibiting excess and shortage in the fuel supply
amount.
[0015] Meanwhile, since a detailed control method using a DC/DC
converter is not described in the foregoing Patent Document 2, it
is desired that a more efficient control method be actualized.
[0016] Further, in the foregoing DMFC, as a method of supplying
methanol to the fuel electrode, a liquid supply type fuel cell (a
liquid fuel (methanol aqueous solution) is directly supplied to the
fuel electrode) and a vaporization supply type fuel cell (a
vaporized liquid fuel is supplied to the fuel electrode) are
proposed. Of the foregoing, in the vaporization supply type fuel
cell, fuel supply control according to the concentration of fuel
such as in the liquid supply type fuel cell is not able to be
performed, and intermittent fuel supply control is performed
according to the fuel supply cycle. Thereby, in the vaporization
supply type DMFC in particular, the power generation voltage and
the power generation current are difficult to control due to the
intermittent fuel supply control, and it is desired that a stable
power generation operation be actualized.
[0017] A first embodiment of a fuel cell system includes: a power
generation section for performing power generation by being
supplied a fuel and oxidant gas; a fuel supply section for
supplying a liquid fuel to the power generation section side and in
which a supply amount of the liquid fuel is able to be adjusted; a
fuel vaporization section for supplying a gas fuel to the power
generation section by vaporizing the liquid fuel supplied from the
fuel supply section; a temperature detection section for detecting
temperature of the power generation section; and a control section
for performing control so that the temperature of the power
generation section becomes constant by adjusting the supply amount
of the liquid fuel from the fuel supply section based on the
temperature of the power generation section detected by the
temperature detection section.
[0018] A first embodiment of a electronic device includes the
foregoing first fuel cell system.
[0019] In the first fuel cell system and the first electronic
device embodiments, the liquid fuel supplied from the fuel supply
section is vaporized in the fuel vaporization section, and
therefore the gas fuel is supplied to the power generation section.
Further, in the power generation section, power generation is
performed by the gas fuel and oxidant gas being supplied. In
addition, the temperature of the power generation section according
to such a power generation is detected by the temperature detection
section. Then, the supply amount of the liquid fuel from the fuel
supply section is adjusted based on the detected temperature of the
power generation section, and therefore control is performed so
that the temperature of the power generation section becomes
constant. Here, the fuel supply amount and the temperature of the
power generation section have a monotonic-increase relationship
with each other. Thus, power generation current, or generated
power, for example, fuel supply control that prevents a crossover
phenomenon and is according to changes in the external environment
is facilitated. Further, since feedback control in which the
temperature of the power generation section becomes constant is
performed, compared to a simple control by turning on (carrying
out) and off (stopping) fuel supply, the temperature of the power
generation section is stabilized.
[0020] A second embodiment of a fuel cell system includes: a power
generation section for performing power generation by being
supplied a fuel and oxidant gas; a fuel supply section for
supplying a liquid fuel to the power generation section side and in
which a supply amount of the liquid fuel is able to be adjusted; a
fuel vaporization section for supplying a gas fuel to the power
generation section by vaporizing the liquid fuel supplied from the
fuel supply section; a boost circuit for raising a power generation
voltage level supplied from the power generation section; and a
control section for performing control on a load voltage and a load
current supplied from the boost circuit to a load by controlling
operation of the boost circuit using a given control table.
[0021] A second embodiment of a electronic device includes the
foregoing second fuel cell system.
[0022] In the second fuel cell system and the second electronic
device, the liquid fuel supplied from the fuel supply section is
vaporized in the fuel vaporization section, and therefore the gas
fuel is supplied to the power generation section. Further, in the
power generation section, power generation is performed by the gas
fuel and oxidant gas being supplied. In addition, the level of the
power generation voltage supplied from the power generation section
by such a power generation is raised by the boost circuit and
supplied to a load as the load voltage. At this time, the load
voltage and the load current supplied from the boost circuit to the
load is controlled by controlling the operation of the boost
circuit using a given control table.
[0023] According to the fuel cell system or the first electronic
device, the supply amount of the liquid fuel from the fuel supply
section is adjusted based on the detected temperature of the power
generation section, and therefore control in which the temperature
of the power generation section becomes constant is performed.
Thus, fuel supply control that prevents the crossover phenomenon
and is according to changes in the external environment is
facilitated and, in addition, the temperature of the power
generation section is stabilized. In result, power generation is
able to be more stably performed regardless of the external
environment.
[0024] According to the second fuel cell system or the second
electronic device, the level of the power generation voltage
supplied from the power generation section is raised by the boost
circuit, and operation of the boost circuit is controlled using a
given control table, and therefore control is performed on the load
voltage and the load current supplied from the boost circuit to the
load. Thus, even in a case where intermittent fuel supply is
performed in a vaporization supply type fuel cell, efficient
control of the load voltage and the load current is actualized. In
result, power generation in the vaporization supply type fuel cell
is able to be more stably performed than in the past.
[0025] Additional features and advantages are described herein, and
will be apparent from, the following Detailed Description and the
figures.
BRIEF DESCRIPTION OF THE FIGURES
[0026] FIG. 1 is a block diagram illustrating a whole structure of
a fuel cell system according to a first embodiment.
[0027] FIG. 2 is a cross sectional view illustrating a structural
example of the power generation section illustrated in FIG. 1.
[0028] FIG. 3 is a plan view illustrating a structural example of
the power generation section illustrated in FIG. 1.
[0029] FIG. 4 is a characteristics diagram for explaining summary
of a vaporized fuel supply method.
[0030] FIG. 5 is a block diagram for explaining a detailed
structure of the control section illustrated in FIG. 1.
[0031] FIG. 6 is a cross sectional view for explaining a method of
manufacturing the power generation section illustrated in FIG.
1.
[0032] FIG. 7 is a plan view for explaining a method of
manufacturing the power generation section illustrated in FIG.
1.
[0033] FIG. 8 is a characteristics diagram illustrating an example
of power generation characteristics by the fuel supply control
according to a comparative example 1.
[0034] FIG. 9 is a schematic characteristics diagram for explaining
power generation characteristics by the fuel supply control
according to a comparative example 2.
[0035] FIG. 10 is a schematic characteristics diagram for
explaining summary of power generation characteristics by the fuel
supply control according to the first embodiment.
[0036] FIG. 11 is a schematic characteristics diagram for
explaining power generation characteristics by the fuel supply
control according to a comparative example 3.
[0037] FIG. 12 is a schematic characteristics diagram for
explaining the details of power generation characteristics by the
fuel supply control according to the first embodiment.
[0038] FIG. 13 is a characteristics diagram illustrating an example
of power generation characteristics by the fuel supply control
according to the first embodiment.
[0039] FIG. 14 is a characteristics diagram illustrating another
example of power generation characteristics by the fuel supply
control according to the first embodiment.
[0040] FIG. 15 is a characteristics diagram illustrating another
example of power generation characteristics by the fuel supply
control according to the first embodiment.
[0041] FIG. 16 is a characteristics diagram illustrating another
example of power generation characteristics by the fuel supply
control according to the first embodiment.
[0042] FIG. 17 is a block diagram for explaining a detailed
structure of the control section according to a second
embodiment.
[0043] FIG. 18 is a characteristics diagram for explaining high
heat generation that may possibly occur in the fuel supply control
according to the first embodiment.
[0044] FIG. 19 is a block diagram for explaining a detailed
structure of the control section according to a comparative example
4.
[0045] FIG. 20 is a characteristics diagram illustrating an example
of power generation characteristics by the fuel supply control
according to a comparative example 4.
[0046] FIG. 21 is a characteristics diagram illustrating an example
of power generation characteristics by the fuel supply control
according to the second embodiment.
[0047] FIG. 22 is a characteristics diagram illustrating another
example of power generation characteristics by the fuel supply
control according to the second embodiment.
[0048] FIG. 23 is a characteristics diagram illustrating an example
of power generation characteristics by the fuel supply control
according to a variation example of the second embodiment.
[0049] FIG. 24 is a diagram illustrating a whole structure of a
fuel cell system according to a third embodiment.
[0050] FIG. 25 is a schematic diagram for explaining operation of
the boost circuit illustrated in FIG. 24.
[0051] FIG. 26 is a timing waveform diagram for explaining summary
of the vaporized fuel supply method.
[0052] FIG. 27 is a circuit diagram illustrating the structures of
the boost circuit and the voltage division circuit illustrated in
FIG. 24.
[0053] FIG. 28 is a timing waveform diagram for explaining a PWM
signal generation operation.
[0054] FIG. 29 is a circuit diagram for explaining operation of the
boost circuit illustrated in FIG. 27.
[0055] FIG. 30 is a timing waveform diagram for explaining a
constant voltage operation according to the third embodiment.
[0056] FIG. 31 is a characteristics diagram illustrating an example
of the constant voltage operation according to the third
embodiment.
[0057] FIG. 32 is a timing waveform diagram for explaining a
constant current operation according to the third embodiment.
[0058] FIG. 33 is a characteristics diagram illustrating an example
of the constant current operation according to the third
embodiment.
[0059] FIG. 34 is a diagram illustrating an example of a control
table used in the constant voltage operation or the constant
current operation according to the third embodiment.
[0060] FIG. 35 is a characteristics diagram illustrating an example
of relation between generated power and the constant voltage
operation or the constant current operation according to the third
embodiment.
[0061] FIG. 36 is a characteristics diagram illustrating an example
of relation between fuel conversion efficiency and the constant
voltage operation or the constant current operation according to
the third embodiment.
DETAILED DESCRIPTION
[0062] Embodiments will be hereinafter described in detail with
reference to the drawings.
First Embodiment
[0063] FIG. 1 illustrates a whole structure of a fuel cell system
(fuel cell system 5) according to a first embodiment. The fuel cell
system 5 supplies electric power for driving a load 6 through
output terminals T2 and T3. The fuel cell system 5 is composed of a
fuel cell 1, a temperature detection section 30, a current
detection section 31, a voltage detection section 32, a boost
circuit 33, a secondary battery 34, and a control section 35.
[0064] The fuel cell 1 includes a power generation section 10, a
fuel tank 40, and a fuel pump 42. For the detailed structure of the
fuel cell 1, a description will be given later.
[0065] The power generation section 10 is a direct methanol power
generation section for performing power generation by reaction
between methanol and oxidant gas (for example, oxygen). The power
generation section 10 includes a plurality of unit cells having a
cathode (oxygen electrode) and an anode (fuel electrode). For the
detailed structure of the power generation section 10, a
description will be given later.
[0066] The fuel tank 40 stores a liquid fuel necessary for power
generation (for example, methanol or methanol aqueous solution).
For the detailed structure of the fuel tank 40, a description will
be given later.
[0067] The fuel pump 42 is a pump for pumping up the liquid fuel
contained in the fuel tank 40 and supplying (transporting) the
liquid fuel to the power generation section 10 side. The fuel pump
42 is able to adjust fuel supply amount of the fuel. Further, such
operation (supply operation of the liquid fuel) of the fuel supply
pump 42 is controlled by the after-mentioned control section 35.
For the detailed structure of the fuel pump 42, a description will
be given later.
[0068] The temperature detection section 30 detects temperature
(specifically, the temperature surrounding or near the power
generation section 10) T1 of the power generation section 10 and
is, for example, composed of a thermistor.
[0069] The current detection section 31 is arranged between the
cathode side of the power generation section 10 and a connection
point P1 on a connection line L1H and is intended to detect a power
generation current I1 of the power generation section 10. The
current detection section 31 includes, for example, a resistor. The
current detection section 31 may be arranged on a connection line
L1L (between the anode side of the power generation section 10 and
a connection point P2).
[0070] The voltage detection section 32 is arranged between the
connection point P1 on the connection line L1H and the connection
point P2 on the connection line L1L. The voltage detection section
32 is intended to detect a power generation voltage V1 of the power
generation section 10. The voltage detection section 32 includes,
for example, a resistor.
[0071] The boost circuit 33 is arranged between the connection
point P1 on the connection line L1H and a connection point P3 on an
output line LO. The boost circuit 33 is a voltage converter that
raises the level of the power generation voltage V1 (DC voltage) of
the power generation section 10 and generates a DC voltage V2. The
boost circuit 33 is composed of, for example, a DC/DC
converter.
[0072] The secondary battery 34 is arranged between the connection
point P3 on the output line LO and a connection point P4 on a
ground line LG. The secondary battery 34 is intended to perform
electric storage based on the DC voltage V2 generated by the boost
circuit 33. The secondary battery 34 is composed of a lithium ion
secondary battery or the like.
[0073] The control section 35 is intended to adjust supply amount
of the liquid fuel from the fuel pump 42 based on the temperature
(detected temperature) T1 of the power generation section detected
by the temperature detection section 30, the power generation
current (detected current) I1 detected by the current detection
section 31 and the power generation voltage (detected voltage) V1
detected by the voltage detection section 32. Specifically, in this
embodiment in particular, the control section 35 is intended to
perform control so that the temperature of the power generation
section 10 becomes constant (almost constant, within a given range)
by the supply amount of the liquid fuel from the fuel pump 42 being
adjusted based on the detected temperature T1 detected by the
temperature detection section 30. The control section 35 is
composed of, for example, a micro computer. For the detailed
structure and detailed operation of the control section 35, a
description will be given later.
[0074] Next, a description will be given of a detailed structure of
the fuel cell 1 with reference to FIG. 2 to FIG. 4. FIG. 2 and FIG.
3 illustrate a structural example of unit cells 10A to 10F in the
power generation section 10 in the fuel cell 1. FIG. 2 corresponds
to a cross sectional structure taken along line II-II of FIG. 3.
The unit cells 10A to 10F are arranged, for example, in a matrix of
three by two in the in-plane direction, and have a planar laminated
structure in which each thereof is electrically connected to each
other in series by a plurality of connection members 20. A terminal
20A as an extension section of the connection members 20 is
attached to the unit cells 10C and 10F. Further, below the unit
cells 10A to 10F, the fuel tank 40, the fuel pump 42, a nozzle 43,
and a fuel vaporization section 44 are provided.
[0075] The unit cells 10A to 10F each have a fuel electrode (anode,
anode electrode) 12 and an oxygen electrode 13 (cathode, cathode
electrode) that are oppositely arranged with an electrolyte film 11
in between.
[0076] The electrolyte film 11 is made of, for example, a proton
conductive material having a sulfonate group (--SO.sub.3H).
Examples of proton conductive materials include a
polyperfluoroalkyl sulfonic acid proton conductive material (for
example, "Nafion (registered trademark)," Du Pont make), a
hydrocarbon system proton conductive material such as polyimide
sulfone acid, and a fullerene system proton conducive material.
[0077] The fuel electrode 12 and the oxygen electrode 13 have, for
example, a structure in which a catalyst layer containing a
catalyst such as platinum (Pt) and ruthenium (Ru) is formed on a
current collector made of, for example, carbon paper. The catalyst
layer is, for example, a layer in which a supporting body such as
carbon black supporting a catalyst is dispersed in a
polyperfluoroalkyl sulfonic acid proton conductive material or the
like. An air supply pump (not illustrated) may be connected to the
oxygen electrode 13. Otherwise, the oxygen electrode 13 may
communicate with outside through an aperture (not illustrated)
provided in the connection member 20, and air, that is, oxygen may
be supplied therein by natural ventilation.
[0078] The connection member 20 has a bend section 23 between two
flat sections 21 and 22. The flat section 21 is contacted with the
fuel electrode 12 of one unit cell (for example, 10A), and the flat
section 22 is contacted with the oxygen electrode 13 of an adjacent
unit cell (for example, 10B), and thereby the adjacent two unit
cells (for example, 10A and 10B) are electrically connected in
series. Further, the connection member 20 has a function as a
current collector to collect electricity generated in the
respective unit cells 10A to 10F. Such a connection member 20 has,
for example, a thickness of 150 .mu.m, is composed of copper (Cu),
nickel (Ni), titanium (Ti), or stainless steel (SUS), and may be
plated with gold (Au), platinum (Pt) or the like. Further, the
connection member 20 has an aperture (not illustrated) for
respectively supplying a fuel and air to the fuel electrode 12 and
the oxygen electrode 13. The connection member 20 is made of mesh
such as an expanded metal, a punching metal or the like. The bend
section 23 may be previously bent according to the thickness of the
unit cells 10A to 10F. Otherwise, in the case where the connection
member 20 is made of a material having flexibility such as mesh
having a thickness of 200 .mu.m or less, the bend section 23 may be
formed by being bent in a manufacturing step. Such a connection
member 20 is joined with the unit cells 10A to 10F by, for example,
screwing a sealing material (not illustrated) such as PPS
(polyphenylene sulfide) and silicon rubber provided around the
electrolyte film 11 into the connection member 20.
[0079] The fuel tank 40 is, for example, composed of a container
with a cubic volume changeable without intrusion of air bubbles or
the like therein even if the liquid fuel 41 is increased or
decreased (for example, a plastic bag), and a rectangular solid
case (structure) to cover the container. The fuel tank 40 is
provided with the fuel pump 42 for suctioning the liquid fuel 41 in
the fuel tank 40 and ejecting the suctioned liquid fuel 41 from the
nozzle 43 in a position above approximately center of the fuel tank
40.
[0080] The fuel pump 42 includes, for example, a piezoelectric body
(not illustrated), a piezoelectric body support resin section (not
illustrated) for supporting the piezoelectric body, and a flow path
(not illustrated) as a pipe to connect the fuel tank 40 with the
nozzle 43. For example, as illustrated in FIG. 4, the fuel pump 42
is able to adjust the supply amount of fuel according to a change
in the fuel supply amount per one operation or a change in the fuel
supply cycle .DELTA.t. The fuel pump 42 corresponds to a specific
example of a "fuel supply section" of the present embodiment.
[0081] The fuel vaporization section 44 is intended to vaporize the
liquid fuel supplied from the fuel pump 42 and thereby to supply
the vaporized fuel to the power generation section 10 (respective
unit cells 10A to 10F). The fuel vaporization section 44 is
structured by providing a diffusion section (not illustrated) for
promoting diffusion of the fuel on a plate (not illustrated) made
of, for example, a metal or an alloy containing stainless steel,
aluminum, or the like, or a resin material with high rigidity, such
as cycloolefin copolymer (COC). As the diffusion section, an
inorganic porous material such as alumina, silica, and titanium
oxide or a resin porous material is able to be used.
[0082] The nozzle 43 is an ejection hole of the fuel transported
through the flow path (not illustrated) of the fuel pump 42, and
ejects the fuel toward the diffusion section provided on the
surface of the fuel vaporization section 44. Thereby, the fuel
transported to the fuel vaporization section 44 is diffused and
vaporized, and is supplied to the power generation section 10
(respective unit cells 10A to 10F). The nozzle 43 has a bore with a
diameter from 0.1 mm to 0.5 mm both inclusive, for example.
[0083] Next, a detailed structure of the control section 35 will be
described with reference to FIG. 5. FIG. 5 illustrates a detailed
block structure of the control section 35.
[0084] The control section 35 is composed of a subtraction section
(difference calculation section) 350, a PID control section 351,
and a heat generation correction section 352.
[0085] The subtraction section 350 is intended to determine a
difference value (=Tsv(s)-Tpv(s)) between a target temperature
(setting temperature) Tsv(s) previously set in the control section
35 or inputted from outside, and a temperature (detected
temperature) T1 (Tpv(s)) of the power generation section 10
detected by the temperature detection section 30, and output the
difference value to the PID control section 351.
[0086] The PID control section 351 is intended to calculate the
supply amount of the liquid fuel (desired heat generation amount
H(s)) by proportioning with a time integral and a time derivative
of the difference value between the target temperature Tsv(s) and
detected temperature Tpv(s) determined in the subtraction section
350, and output the desired heat generation amount H(s) to the heat
generation correction section 352.
[0087] Specifically, the PID control section 351 calculates the
desired heat generation amount H(s) using the following Equation
(1) and Equation (2).
H(s)=K.sub.P.DELTA.T(s)+T.sub.I.intg..DELTA.T(s)ds+T.sub.D{d.DELTA.T(s)/-
ds} (1)
.DELTA.T(s)=Tsv(s)-Tpv(s) (2)
[0088] In the equations, H(s) represents desired heat generation
amount; K.sub.P, T.sub.I, and T.sub.D represent PID constants;
Tsv(s) represents target temperature; .DELTA.T(s) represents
difference in temperature; and s represents time.
[0089] The heat generation correction section 352 is intended to
calculate energy conversion efficiency in the power generation
section 10 based on the power generation voltage (detected voltage)
V1 detected by the voltage detection section 32 and the power
generation current (detected current) I1 detected by the current
detection section 31, and calculate a fuel supply amount P(s)
(corrects the supply amount of the liquid fuel calculated in the
PID control section 351) using the calculated energy conversion
efficiency. Information on the fuel supply amount P(s) is output to
the fuel pump 42 in the fuel cell 1. In result, although details
will be described hereafter, the temperature of the power
generation section 10 becomes constant.
[0090] Specifically, the heat generation correction section 352
calculates the fuel supply amount P(s) using the following Equation
(3) and Equation (4). In this embodiment, energy conversion
efficiency .eta. in the power generation section 10 is calculated
also taking into consideration the power generation current I1 of
the power generation section 10 in addition to the power generation
voltage V1 of the power generation section 10. However, the energy
conversion efficiency .eta. in the power generation section 10 may
be approximately calculated (.eta..apprxeq.V.sub.O/V.sub.T) by
performing an approximation that usage rate E of fuel is almost 1.
This is because in actual control, control operation is barely
affected, even if such an approximate calculation is performed.
P(s)(=P.sub.PID(s))=H(s).times.(1-.eta.) (3)
.eta.={(V.sub.OI.sub.O)/(V.sub.TI.sub.T)}=(V.sub.O/V.sub.T).times.E
(4)
I.sub.T represents a theoretical current value estimated from the
fuel supply amount.
[0091] The fuel cell system 5 of this embodiment is able to be
manufactured, for example, as follows.
[0092] First, the electrolyte film 11 made of the foregoing
material is sandwiched between the fuel electrode 12 and the oxygen
electrode 13 made of the foregoing material. The resultant is
joined by thermal compression bond. Thereby, the fuel electrode 12
and the oxygen electrode 13 are joined with the electrolyte film 11
to form the unit cells 10A to 10F.
[0093] Next, the connection member 20 made of the foregoing
material is prepared. As illustrated in FIG. 6 and FIG. 7, the six
unit cells 10A to 10F are arranged in a matrix of three by two, and
are electrically connected to each other in series by the
connection member 20. The sealing material (not illustrated) made
of the foregoing material is provided around the electrolyte film
11, and the sealing material is screwed and fixed on the bend
section 23 of the connection member 20.
[0094] After that, the fuel tank 40 that contains the liquid fuel
41 and is provided with the fuel pump 42, the nozzle 43 and the
like is arranged on the fuel electrode 12 side of the linked unit
cells 10A to 10F, and therefore the fuel cell 1 is formed. The
foregoing temperature detection section 30, the current detection
section 31, the voltage detection section 32, the boost circuit 33,
the secondary battery 34, and the control section 35 are
electrically connected in parallel to the fuel cell 1 respectively
as illustrated in FIG. 1. Accordingly, the fuel cell system 5
illustrated in FIG. 1 to FIG. 3 is completed.
[0095] Next, a description will be given in detail of action and
effect of the fuel cell system 5 of this embodiment, while
comparing the fuel cell system 5 with comparative examples.
[0096] In the fuel cell system 5, the liquid fuel 41 contained in
the fuel tank 40 is pumped up by the fuel pump 42, and therefore
the liquid fuel 41 passes through the flow path (not illustrated)
and reaches the fuel vaporization section 44. In the fuel
vaporization section 44, in the case where the liquid fuel is
ejected by the nozzle 43, the fuel is diffused over a wide range by
the diffusion section (not illustrated) provided on the surface
thereof. Thereby, the liquid fuel 41 is naturally vaporized, and
the vaporized fuel is supplied to the power generation section 10
(specifically, the fuel electrodes 12 of the respective unit cells
10A to 10F).
[0097] Meanwhile, air (oxygen) is supplied to the oxygen electrode
13 of the power generation section 10 by natural ventilation or an
air supply pump (not illustrated). Then, in the oxygen electrode
13, reaction shown in the following Expression (5) is generated,
and hydrogen ions and electrons are generated. The hydrogen ions
reach the fuel electrode 12 through the electrolyte film 11. In the
fuel electrode 12, reaction shown in the following Expression (6)
is generated, and water and carbon dioxide are generated. Thus, as
the entire fuel cell 1, reaction shown in the following Expression
(7) is generated, and power generation is performed.
CH.sub.3OH+H.sub.2O.fwdarw.CH.sub.26H.sup.++6e.sup.- (5)
6H.sup.++(3/2)O.sub.2+6e.sup.-.fwdarw.3H.sub.2O (6)
CH.sub.3OH+(3/2)O.sub.2.fwdarw.CO.sub.2+2H.sub.2O (7)
[0098] Thereby, part of chemical energy of the liquid fuel 41, that
is, methanol is converted to electric energy, which is collected by
the connection member 20 and is extracted as a current (power
generation current I1) from the power generation section 10. The
level of the power generation voltage (DC voltage) V1 based on the
power generation current I1 is raised (voltage conversion) by the
boost circuit 33 and becomes the DC voltage V2. The DC voltage V2
is supplied to the secondary battery 34 or a load (for example, an
electronic device body). In the case where the DC voltage V2 is
supplied to the secondary battery 34, the secondary battery 34 is
charged based on the voltage. Meanwhile, in the case where the DC
voltage V2 is supplied to the load 6 through the output terminals
T2 and T3, the load 6 is driven, and given operation is made. At
this time, in the fuel pump 42, the supply amount of fuel is
adjusted according to a change in the fuel supply amount per one
operation or a change in the fuel supply cycle .DELTA.t under the
control of the control section 35.
[0099] Here, in a past fuel supply control of a comparative example
1, the foregoing fuel supply cycle .DELTA.t is constant at all
times. In this case, a loop that is "output
increases.fwdarw.temperature increases.fwdarw.electrolyte film 11
becomes dry.fwdarw.output decreases.fwdarw.temperature
decreases.fwdarw.electrolyte film 11 becomes moist.fwdarw. . . . "
is continuously repeated. Thereby, for example, as illustrated in
FIG. 8, power generation output and temperature varies
significantly regardless of the fuel supply being at a constant
interval.
[0100] Further, in a past fuel supply control of a comparative
example 2, two threshold values (an upper limit value and a lower
limit value) are set for the power generation voltage during
constant current power generation control and for the power
generation current during constant voltage power generation
control, and the fuel supply is stopped when the upper limit value
is exceeded. Meanwhile, the fuel supply is resumed when the value
falls below the lower limit value. However, for example, as
illustrated in FIG. 9, the fuel supply amount, the power generation
voltage, the power generation current, and the power generation
output that is the product of the foregoing do not indicate change
that is monotonic with each other, and a mountain-shaped curve is
drawn in which the power generation voltage and the like have a
maximal value according to increase in the fuel supply amount.
Therefore, for example, in the case where the power generation
voltage is low, since it is not possible to know whether the
maximal value (threshold value) is exceeded at that point, an
accurate determination of whether to increase or decrease fuel
supply is not able to be made. Specifically, for example, in the
case where the crossover phenomenon occurs, the situation is
worsened. In other words, for example, while the voltage decreases
and falls below the lower limit value when fuel is insufficient
during constant current control, since the voltage similarly
decreases when the crossover phenomenon occurs as well, the voltage
falls below the lower limit value. Here, in the former (when fuel
is insufficient), it is necessary to supply fuel, while in the
latter (when crossover phenomenon occurs), it is necessary to stop
fuel supply. However, since focus is placed merely on voltage in
the fuel supply control of the comparative example 2, the
difference between the former and the latter is not able to be
differentiated.
[0101] Meanwhile, in the fuel cell system 5 of this embodiment, as
illustrated in FIG. 1 and FIG. 5, the temperature (detected
temperature) T1 of the power generation section 10 is detected by
the temperature detection section 30, and the supply amount of the
liquid fuel by the fuel pump 42 is adjusted by the control section
35 based on the detected temperature T1. Here, unlike the foregoing
power generation voltage and the like, the fuel supply amount and
the temperature of the power generation section have a
monotonic-increase relationship with each other, as illustrated in
FIG. 10, for example.
[0102] Thereby, compared to the fuel supply control based on the
power generation voltage and the like such as in the comparative
example 1, for example, fuel supply control that prevents the
crossover phenomenon and is according to changes in the external
environment is facilitated (for example, threshold values such as
those illustrated in FIG. 10 are more easily defined).
Specifically, all that is needed is to reduce fuel supply every
time when the detected temperature T1 is too high and, on the
contrary, increase fuel supply every time when the detected
temperature T1 is too low. Since a situation that causes failure is
not present according to this principle, highly stable and robust
power generation is able to be continued.
[0103] Further, to begin with, the fuel cell generates power by
chemical reaction. Oxidation reaction of the fuel progresses in the
fuel electrode and reductive reaction of the oxidant progresses in
the oxygen electrode. Thus, controlling power generation is nothing
other than controlling the chemical reaction itself. Here,
according to chemical reaction kinetics, parameters determining a
chemical reaction rate are frequency factor, activation energy, and
temperature. Considering that the two former parameters are almost
constants, it is clear that stabilizing the temperature is
important for stabilizing the chemical reaction of the fuel cell.
Therefore, from such a perspective as well, stable power generation
is able to be actualized by stabilizing temperature, which is a
basic control parameter for determining the power generation
current.
[0104] However, it cannot be said that a simple control in which,
when fuel supply is performed based on the detected temperature T1,
the fuel supply is stopped when the upper limit temperature is
exceeded, while the fuel supply is resumed when the temperature
falls below the lower limit temperature, is ideal. In this case, in
a similar manner to temperature control by a thermostat using
bimetal, for example, as in a comparative example 3 illustrated in
FIG. 11(A) and FIG. 11(B), the possibility of the temperature
fluctuating significantly is high. In other words, stopping the
fuel supply after the upper limit temperature is exceeded is too
late, and the temperature T1 of the power generation section 10
further increases. Meanwhile, resuming the fuel supply after the
temperature falls below the lower limit temperature is also too
late, and the temperature T1 of the power generation section 10
further decreases.
[0105] Thus, in the fuel cell system 5 of this embodiment, as
illustrated in FIG. 5, feedback control (specifically, PID control)
in which the temperature of the power generation section 10 becomes
constant is performed by the PID control section 351. The PID
control is a classical feedback control method that is able to
quickly bring a control amount closer to a target value and
stabilize the control amount, and is a control method that is able
to smoothly bring the control amount closer to an actual target
value.
[0106] In result, for example, as illustrated in FIG. 12(A) and
FIG. 12(B), overshooting and undershooting of the temperature of
the power generation section 10 are prevented. Compared to the
simple control by turning on (carrying out) and off (stopping) the
fuel supply described in the foregoing comparative example 3, the
temperature of the power generation section 10 stabilizes. Thereby,
for example, as illustrated in FIG. 13, it is clear that the power
generation operation is stably performed in the power generation
section 10 by the fuel supply control of this embodiment.
[0107] In addition, for example, in an example illustrated in FIG.
14(A) to FIG. 14(D), rather than directly supplying the calculated
fuel supply amount, a power generation test is performed by adding
noise to the calculation result (power generation result when
changes are made from noise added.fwdarw.no noise.fwdarw.noise
added). According to FIG. 14, it is clear that the power generation
output is barely affected even when noise is added, and power
generation is stably continued. In a fuel cell system using a fuel
pump as a fuel supply means, the injection amount may possibly
change as a result of decay with age of the fuel pump and
disturbance. However, the results illustrated in FIG. 14 indicate
power generation is stably continued even when the injection amount
of the fuel pump unexpectedly changes.
[0108] Further, for example, an example illustrated in FIG. 15(A)
to FIG. 15(D) is a case in which the fuel supply amount is suddenly
significantly changed (here, when suddenly reduced). According to
FIG. 15, it is clear that, even if the fuel supply amount is
suddenly significantly changed, the change is mostly able to be
absorbed by PID control.
[0109] Further, for example, an example illustrated in FIG. 16(A)
to FIG. 16(D) is a case in which air bubbles are mixed in the
liquid fuel. According to FIG. 16, it is clear that, even if some
air bubbles are mixed in the fuel electrode, the change is mostly
able to be absorbed by PID control.
[0110] As described above, in this embodiment, control in which the
temperature T1 of the power generation section 10 becomes constant
is performed by adjusting the supply amount of the liquid fuel from
the fuel pump 42 based on the temperature T1 of the power
generation section 10 detected by the temperature detection section
30. Thereby, compared to the past, for example, fuel supply control
that prevents the crossover phenomenon and is according to changes
in the external environment is facilitated and, in addition, the
temperature of the power generation section 10 is stabilized. Thus,
power generation is able to be more stably performed than in the
past, regardless of the external environment (for example, decay
with age and disturbances).
[0111] Specifically, in the PID control section 351, control in
which the temperature of the power generation section 10 becomes
constant is performed by proportioning the supply amount of the
liquid fuel with the time integral and the time derivative of the
difference value between the target temperature Tsv(s) and the
detected temperature T1 (Tpv(s)). Thus, the foregoing effect is
able to be obtained.
[0112] Further, in the heat generation correction section 352, the
energy conversion efficiency .eta. in the power generation section
10 is calculated based on the power generation voltage V1 detected
by the voltage detection section 32 and the power generation
current I1 detected by the current detection section 31, and the
supply amount of the liquid fuel is corrected using the calculated
energy conversion efficiency .eta.. Thus, fuel supply control
taking into consideration the energy conversion efficiency .eta.
becomes possible, and power generation that is more stable than
that in the past is able to be performed.
[0113] Further, even in a vaporization supply type DMFC in which
stable power generation operation independent of the external
environment is particularly desired, power generation is able to be
performed more stably than in the past by inhibiting excess and
shortage of the fuel supply amount.
Second Embodiment
[0114] Next, a second embodiment will be described. A fuel cell
system of this embodiment is the fuel cell system 5 of the first
embodiment illustrated in FIG. 1 in which an after-mentioned
control section 36, described hereafter, is provided in place of
the control section 35. Thus, the same symbols are affixed to the
elements similar to those of the foregoing first embodiment, and
the description thereof will be omitted as appropriate.
[0115] FIG. 17 illustrates a block structure of the control section
36 of this embodiment. The control section 36 is composed of the
subtraction section (difference calculation section) 350, the PID
control section 351, the heat generation correction section 352, a
usage rate control section 361, and a minimum value selection
section 362. In other words, the usage rate control section 361 and
the minimum value selection section 362 are further provided in the
control section 35 of the first embodiment illustrated in FIG.
5.
[0116] The usage rate control section 361 calculates a usage rate E
(=actual power generation current value I.sub.O/theoretical current
value I.sub.T estimated from the fuel supply amount) of fuel in the
power generation section 10 based on the power generation current
(detected current) I1 detected by the current detection section 31
and calculates a supply amount P.sub.E(s) of the liquid fuel so
that the calculated usage rate E of the fuel is maintained (becomes
constant). Since an electric charge of 6e.sup.- is extracted per
one methanol molecule, the usage rate E of fuel refers to a ratio
of a measured current (here, the detected current I1) to a
theoretical maximum current, calculated based on this relation.
[0117] Specifically, the usage rate control section 361 calculates
the fuel supply amount P.sub.E(s) using the following Equation
(8).
P.sub.E(s)=Kcell.times.Esv.times.Ipv(s) (8)
[0118] (Kcell represents a constant of proportion; Esv represents a
setting value of the usage rate; and Ipv(s) represents a current
power generation current value)
[0119] The minimum value selection section 362 determines a final
fuel supply amount P(s), taking into consideration the fuel supply
amount P.sub.PID(s) (first fuel supply amount) calculated based on
the temperature T1 of the power generation section 10 in the PID
control section 351 and the heat generation correction section 352,
and the fuel supply amount P.sub.E(s) (second fuel supply amount)
calculated based on the usage rate E of the fuel in the usage rate
control section 361, and supplies the final fuel supply amount P(s)
to the fuel pump 42 in the fuel cell 1. Specifically, the final
fuel supply amount P(s) is determined by selecting one of the fuel
supply amount P.sub.PID(s) and the fuel supply amount P.sub.E(s).
More specifically, the final fuel supply amount P(s) is determined
by selecting the smaller supply amount value of the fuel supply
amount P.sub.PID(s) and the fuel supply amount P.sub.E(s).
[0120] Another selection method may be used instead of the
selection method in the minimum value selection section 36. For
example, the final fuel supply amount P(s) may be determined by
selecting one of the fuel supply amount P.sub.PID(s) and the fuel
supply amount P.sub.E(s) depending on the type of power generation
mode in the power generation section 10.
[0121] Next, a description will be given in detail of action and
effect of the fuel cell system of this embodiment. Basic operation
of the fuel cell system is similar to that of the first embodiment,
and thereby only the control operation for fuel supply by the
control section 36 will be described.
[0122] First, in the forgoing control section 35 of the first
embodiment, for example, in the case where the fuel cell 1 that is
generating power is suddenly cooled, a large high heat generation
phenomenon may possibly occur, as illustrated in FIG. 18 for
example, for the following reason. That is, since the target
temperature is constant at all times, if the fuel cell 1 is
continuously cooled from the outside and cannot reach the target
temperature, the control section 35 attempts to approach the target
temperature even by performing excessive fuel supply and causing a
crossover phenomenon. In other words, although the fuel cell 1 is
in a situation where power is not able to be generated, this
situation is not recognized.
[0123] Thereby, for example, such as in a control section 106
(comparative example 4) illustrated in FIG. 19, providing the
foregoing usage rate control section 361 in the control section
106, and adjusting the supply amount P.sub.E(s) of the liquid fuel
so that the calculated usage rate of fuel becomes constant can be
considered. According to this, for example, even if sudden cooling
and the like occur, it is thought that the changes in the
environment are able to be followed.
[0124] In the fuel supply control of the comparative example 4, for
example, as illustrated in FIG. 20(A) to FIG. 20(C), it is clear
that power generation is able to be continued without decrease in
the usage rate (maintained at about 50%) even if cooling is
performed by sending air around the power generation section 10
during power generation (when sudden cooling occurs). However, as
illustrated in FIG. 20(C), the temperature of the power generation
section 10 rises to a maximum of almost 60.degree. C., and a high
temperature phenomenon occurs.
[0125] Meanwhile, in the control section 36 of this embodiment, the
final fuel supply amount P(s) is determined taking into
consideration both the fuel supply amount P.sub.PID(s) calculated
based on the temperature T1 of the power generation section 10 in
the PID control section 351 and the heat generation correction
section 352, and the fuel supply amount P.sub.E(s) calculated based
on the usage rate of fuel in the usage rate control section 361. In
other words, the advantage of the PID control in which the
temperature of the power generation section 10 becomes constant and
the advantage of the usage rate control in which the usage rate in
the power generation section 10 becomes constant are both used, and
respective disadvantages are cancelled out.
[0126] In result, for example, in the case where sudden cooling or
the like occurs, the high heat generation phenomenon in the PID
control is prevented since the usage rate E of the power generation
section 10 becomes constant, and the high temperature phenomenon in
the usage rate control is prevented since an upper limit is
provided for the temperature of the power generation section
10.
[0127] Thus, for example, as illustrated in FIG. 21(A) to FIG.
21(D), it is clear that, even if air is sent around the power
generation section 10 and the power generation section 10 is
suddenly cooled, abnormal heat generation resulting from crossover
does not occur and stable power generation is performed. In
addition, for example, as illustrated in FIG. 22(A) to FIG. 22(D),
it is clear that, even if the bottom of the power generation
section 10 is directly cooled, abnormal heat generation resulting
from crossover similarly does not occur and stable power generation
is similarly performed.
[0128] As described above, in this embodiment, the final fuel
supply amount P(s) is determined taking into consideration both the
fuel supply amount P.sub.PID(s) calculated based on the temperature
T1 of the power generation section 10 in the PID control section
351 and the heat generation correction section 352, and the fuel
supply amount P.sub.E(s) calculated based on the usage rate E of
the fuel in the usage rate control section 361. Thereby, the high
heat generation phenomenon in the PID control and the high
temperature phenomenon in the usage rate control are able to be
prevented. Thus, compared to the first embodiment, stable power
generation is able to be performed even under further various
external environment changes.
[0129] Specifically, in the minimum value selection section 362,
the final fuel supply amount P(s) is determined by selecting the
smaller supply amount value of the fuel supply amount P.sub.PID(s)
and fuel supply amount P.sub.E(s). Thereby, the foregoing effect is
able to be obtained.
[0130] Further, the upper limit value (Tmax) of the temperature and
the lower limit value (Emin) of the usage rate of the power
generation section 10 are able to be prescribed by combining the
PID control and the usage rate control, and a stable and robust
power generation operation is able to be actualized against various
disturbances.
Variation Example of the Second Embodiment
[0131] In the fuel supply control of the second embodiment
(combination of the PID control and the usage rate control), when
the setting of the lower limit value of the usage rate E is
unsuitable, it is possible sufficient power generation output is
not able to be obtained or, conversely, fuel is wastefully
consumed. Specifically, as cases where the setting of the lower
limit value of the usage rate E is unsuitable, for example, a case
where the setting of the lower limit value of the usage rate E is
unsuitable for the external environment and the like, and a case
where the fuel supply amount per one operation of the fuel pump 42
changes resulting from failure in the fuel supply system and the
like are given. Thereby, the setting value (here, the lower limit
value) of the usage rate E of the fuel is preferably (dynamically)
updated periodically according to the environment in the control
section 36. Specifically, for example, the fuel is completely
consumed every ten minutes and, in addition, a raw power value of
the usage rate E of the fuel in the last ten minutes is calculated
each time. Then, the lower limit value of the usage rate E is
automatically updated so that the calculated usage rate E is
maintained even during the next ten minutes.
[0132] In this case, for example, as illustrated in FIG. 23(A) to
FIG. 23(F), not only safety, but also energy conversion efficiency
.eta. (fuel economy) is able to be optimized.
Third Embodiment
[0133] FIG. 24 illustrates a whole structure of a fuel cell system
(fuel cell system 5A) of a third embodiment. The fuel cell system
5A supplies electric power for driving the load 6 through the
output terminals T2 and T3. The fuel cell system 5A is composed of
the fuel cell 1, the current detection section 31, the voltage
detection section 32, a boost circuit 33A, a voltage division
circuit 37, the secondary battery 34, and a control section 35A.
The same symbols are affixed to the elements similar to those of
the foregoing first and second embodiments, and the description
thereof will be omitted as appropriate.
[0134] The voltage detection section 32 is arranged between the
connection point P1 on the connection line L1H and the connection
point P2 on the connection line L1L. The voltage detection section
32 is intended to detect the power generation voltage V1 of the
power generation section 10 (input voltage Vin of the boost circuit
33A). The voltage detection section 32 includes, for example, a
resistor.
[0135] The boost circuit 33A is arranged between the connection
point P1 of the connection line L1H and a connection point P5 on
the output line LO. The boost circuit 33A is a voltage converter
that raises the level of the power generation voltage V1 (DC input
voltage Vin) of the power generation section 10 and generates a DC
output voltage Vout. The boost circuit 33A includes, for example, a
DC/DC converter. The boost circuit 33A performs a voltage raising
operation according to a potential comparison result of a divided
voltage V.sub.FB generated by the voltage division circuit 37,
described hereafter, and a given reference voltage (reference
voltage Vref, described hereafter). As a result of such voltage
raising operation by the boost circuit 33A, for example, as
illustrated in FIG. 25, the output voltage Vout is able to become
greater than a terminal voltage LiV of the secondary battery 34 and
a potential difference .DELTA.V is able to be generated. Thereby, a
charging operation of the secondary battery 34 is able to be
performed. Further, a value of the output current lout from the
boost circuit 33A at this time is determined by the foregoing
potential difference .DELTA.V and an internal resistance value of
the secondary battery 34. For the detailed structure and detailed
operation of the boost circuit 33A, a description will be given
later.
[0136] The voltage division circuit 37 is arranged between the
connection point P5 on the output line LO and a connection point 6
on the ground line G, and is composed of resistors R3 and R4, and a
variable resistor Rv. One end of the resistor R3 is connected to
the connection point P5, and the other end is connected to one end
of the variable resistor Rv. In addition, the other end of the
variable resistor Rv is connected to one end of the resistor R4 at
a connection point P7. Further, the other end of the resistor R4 is
connected to the connection point P6. In this case, the voltage
division circuit 37 feeds back to the boost circuit 33A the divided
voltage V.sub.FB (feedback voltage) of the output voltage Vout from
the boost circuit 33A generated between the connection points P6
and P7. For details on the feedback operation, a description will
be given later.
[0137] The secondary battery 34 is arranged between the connection
point P3 on the output line LO and a connection point P4 on the
ground line LG. The secondary battery 34 is intended to perform
electric storage based on the DC output voltage Vout (load voltage)
generated by the boost circuit 33A and the output current lout
(load current) from the boost circuit 33A. The secondary battery 34
is composed of, for example, a lithium ion secondary battery or the
like.
[0138] The control section 35A is intended to adjust the supply
amount of the liquid fuel from the fuel pump 42 based on the power
generation current (detected current) I1 detected by the current
detection section 31 and the power generation voltage (detected
voltage) V1 (input voltage Vin) detected by the voltage detection
section 32. Further, the control section 35A is intended to perform
control on the output voltage Vout (load voltage) and the output
current lout (load current) supplied from the boost circuit 33A to
a load (the secondary battery 34 and the load 6) by controlling the
voltage raising operation of the boost circuit 33A using an
after-mentioned given control table. Such a control section 35A is
composed of a micro computer or the like. For details on the
control operation for the output voltage Vout and the output
current lout by the control section 35A, a description will be
given later.
[0139] The fuel pump 42 includes, for example, a piezoelectric body
(not illustrated), a piezoelectric body support resin section (not
illustrated) for supporting the piezoelectric body, and a flow path
(not illustrated) as a pipe to connect the fuel tank 40 with the
nozzle 43. For example, as illustrated in FIGS. 26(A) and (B), the
fuel pump 42 is able to adjust the supply amount of the fuel
according to a change in the fuel supply amount per one operation
or a change in the fuel supply cycle .DELTA.t. The fuel pump 42
corresponds to a specific example of a "fuel supply section".
[0140] Detailed structures of the boost circuit 33A and the voltage
division circuit 37 will be described with reference to FIG. 27 and
FIG. 28. FIG. 27 illustrates detailed circuit structures of the
boost circuit 33A and the voltage division circuit 37.
[0141] The boost circuit 33A is composed of a DC/DC converter, a
reference power supply 331, an error amplifier 332, an oscillation
circuit 333, and a PWM (pulse width modulation) signal generation
section 334. The DC/DC converter is composed of an inductor 33L, a
capacitor 33C, and two switching elements Tr1 and Tr2.
[0142] The DC/DC converter is a voltage converter that raises the
level of the power generation voltage V1 of the power generation
section 10 (DC input voltage Vin) and generates the DC output
voltage Vout. In the DC/DC converter, the inductor 33L is inserted
and arranged on the connection line L1H. In addition, the switching
element Tr1 is arranged between the connection line L1H and the
connection line L1L, the switching element Tr2 is inserted and
arranged on the connection line L1H and the output line LO, and the
capacitor 33C is arranged between the output line LO and the ground
line LG.
[0143] Here, the switching elements Tr1 and Tr2 are each composed
of, for example, an N-channel MOS-FET (metal oxide
semiconductor-field effect transistor). Control signals (PWM
signals) S1 and S2 output from the after-mentioned PWM signal
generation section 334 are supplied to gate terminals of the
switching elements Tr1 and Tr2, and respective switching operations
are controlled.
[0144] The reference power supply 331 is a power supply for
supplying the reference voltage Vref of the error amplifier
332.
[0145] The error amplifier 332 compares the divided voltage
V.sub.FB supplied by the voltage division circuit 37 and the
reference voltage Vref supplied by the reference power supply 331
for large and small potential difference, and outputs the
comparison result ("H (high)" or "L (low)" signal) to the PWM
signal generation section 334.
[0146] The oscillation circuit 333 generates a pulse signal used
for generating the PWM signal in the PWM signal generation section
334 and supplies the generated pulse signal to the PWM signal
generation section 334.
[0147] The PWM signal generation section 334 generates the control
signals S1 and S2 of the switching elements Tr1 and Tr2 composed of
PWM signals based on the comparison result in the error amplifier
332 and the pulse signal supplied from the oscillation circuit 333.
Specifically, for example, as illustrated in FIGS. 28(A) and (B),
in the case where the divided voltage V.sub.FB has a greater
potential than the reference voltage Vref composed of a saw-shaped
waveform, PWM signals (the control signal S1) having a pulse width
are generated during this period. In addition, at this time, as
indicated by pulse widths .DELTA.t1 to .DELTA.t3 in the figure, the
pulse width of the control signal S1 becomes smaller as the
potential of the divided voltage V.sub.FB becomes greater and,
conversely, the pulse width of the control signal S1 becomes
greater as the potential of the divided voltage V.sub.FB becomes
smaller.
[0148] The fuel cell system 5A of this embodiment is able to be
manufactured, for example, as follows.
[0149] First, the fuel cell 1 is formed in a similar manner to the
method described in the foregoing first embodiment. Then, the
foregoing current detection section 31, voltage detection section
32, boost circuit 33A, voltage division circuit 37, secondary
battery 34, and control section 35A are each electrically connected
and attached to the fuel cell 1, as illustrated in FIG. 24. In
result, the fuel cell system 5A illustrated in FIG. 24 and FIG. 25
is formed.
[0150] Next, a description will be given in detail of action and
effect of the fuel cell system 5A of this embodiment.
[0151] In the fuel cell system 5A, as the entire fuel cell 1,
reaction shown in Expression (7) is generated in a manner similar
to that in the first embodiment, and power generation is
performed.
[0152] Thereby, part of chemical energy of the liquid fuel 41, that
is, methanol is converted to electric energy, which is collected by
the connection member 20 and is extracted as a current (power
generation current I1) from the power generation section 10. The
level of the power generation voltage (DC voltage) V1 (input
voltage Vin) based on the power generation current I1 is raised
(voltage conversion) by the boost circuit 33A and becomes the DC
voltage (output voltage) Vout. The output voltage Vout (load
voltage) and the output current lout (load current) from the boost
circuit 33A are supplied to the secondary battery 34 or a load (for
example, an electronic device body). Then, in the case where the
output voltage Vout and the output current lout are supplied to the
secondary battery 34, the secondary battery 34 is charged based on
the voltage and the current. Meanwhile, in the case where the
output voltage Vout and the output current lout are supplied to the
load 6 through the output terminals T2 and T3, the load 6 is
driven, and given operation is made.
[0153] At this time, in the fuel pump 42, the fuel supply amount
per one operation or the fuel supply cycle .DELTA.t is controlled
by the control section 35A and, accordingly, the fuel supply amount
is adjusted.
[0154] In addition, at this time, in the boost circuit 33A of this
embodiment, more specifically, a voltage raising operation such as
that illustrated in FIG. 29(A) to FIG. 29(C), for example, is
performed. FIG. 29(A) to FIG. 29(C) illustrate the voltage raising
operation of the boost circuit 33A using a circuit state diagram.
The section of the foregoing DC/DC converter in the boost circuit
33A is extracted and illustrated. However, the input voltage Vin is
illustrated as a power supply for convenience, and the load
connected to the output side is illustrated as a load resistor
R.sub.L for convenience. Further, to make the ON and OFF state of
the switching elements Tr1 and Tr2 more understandable, the
switching elements Tr1 and Tr2 are illustrated in the shape of a
switch for convenience.
[0155] In the DC/DC converter in the boost circuit 33A, first, as
illustrated in FIG. 29(A), when the input voltage Vin is supplied,
a current Ia composed of the current flow path illustrated in the
figure flows to the inductor 33L. At this time, the switching
element Tr1 is in an OFF state and the switching element Tr2 is in
an ON state.
[0156] Next, as illustrated in FIG. 29(B), when the switching
element Tr1 enters the ON state, a current IL flowing to the
inductor 33L and the switching element Tr1 becomes greater than the
output current lout flowing to the load resistor R.sub.L. The
current IL increases in this way, and therefore large energy is
stored in the inductor 33L.
[0157] Next, as illustrated in FIG. 29(C), when the switching
element Tr1 once again enters the OFF state, the current Ia
composed of the current flow path illustrated in the figure flows.
At this time, since a current by the energy stored in the inductor
33L is superimposed on the current Ia, the output voltage Vout
supplied to the load resistor R.sub.L is expressed by a following
Equation (9), in the case where the voltage generated at the
inductor 33L is VL. In addition, at this time, the capacitor 33C is
simultaneously charged until the voltage between both ends reaches
the output voltage Vout.
Vout=Vin+VL (9)
[0158] Then, by subsequently repeating the operations in FIG. 29(B)
and FIG. 29(C), an output voltage Vout that is a higher voltage
than the input voltage Vin is generated (voltage raising operation
is performed) and supplied to the load resistor R.sub.L.
[0159] In addition, at this time, the divided voltage V.sub.FB of
the output voltage Vout such as that illustrated in FIG. 28(A) is
fed back to the boost circuit 33A by the voltage division circuit
37. Further, in the PWM signal generation section 334, the control
signals S1 and S2 for the switching elements Tr1 and Tr2 composed
of the PWM signals, such as those illustrated in FIG. 28(B), are
generated based on the comparison result in the error amplifier 332
and the pulse signal supplied from the oscillation circuit 333. At
this time, the pulse width of the control signal S1 becomes smaller
as the potential of the divided voltage V.sub.FB becomes greater
and, conversely, the pulse width of the control signal S1 becomes
greater as the potential of the divided voltage V.sub.FB becomes
smaller.
[0160] Thus, in the case where the output voltage Vout is low, the
operation is that in which the pulse width of the control signal S1
increases and the output voltage Vout is increased. Meanwhile, in
the case where the output voltage Vout is high, the operation is
that in which the pulse width of the control signal S1 decreases
and the output voltage Vout is decreased. Thereby, control is
performed so that the output voltage Vout (load voltage) is
constant (constant voltage operation) by controlling the divided
voltage V.sub.FB to become equal with the reference voltage
Vref.
[0161] Specifically, the constant voltage operation is performed as
illustrated in FIGS. 30(A) to (D) and FIG. 31, for example. In
other words, in a state in which the output voltage Vout (FC
voltage, power generation voltage) is fixed to a constant value,
the output current lout (FC current, power generation current)
increases immediately after the liquid fuel 41 is supplied by the
fuel pump 42 and the FC current gradually decreases with the
decrease in liquid fuel 41. A reason for this is that the amount of
power capable of being generated by the power generation section 10
with a constant amount of liquid fuel 41 is also a constant value.
Thereby, as the intermittently supplied liquid fuel 41 is consumed
by power generation in the power generation section 10, the FC
current from the power generation section 10 decreases.
[0162] In addition, in this embodiment, for example, by feeding
back to the boost circuit 33A the voltage corresponding to the
power generation current (input current) I1, operation control of
the boost circuit 33A is also able to be performed (constant
current operation) so that the output current lout (load current)
becomes constant.
[0163] In this case, specifically, the constant current operation
is performed as illustrated in FIGS. 32(A) to (D) and FIG. 33, for
example. In other words, in this case, the liquid fuel 41 increases
immediately after the liquid fuel 41 is supplied by the fuel pump
42. Thereby, in the state in which the output current lout (FC
current, power generation current) is fixed to a constant value,
the output voltage Vout (FC voltage, power generation voltage)
increases according to the supply amount of the liquid fuel 41.
Meanwhile, the FC voltage decreases as the liquid fuel 41
decreases.
[0164] Here, in this embodiment, in such constant voltage operation
and constant current operation, the voltage raising operation of
the boost circuit 33A is controlled in the control section 35A by
using a control table, such as that illustrated in FIGS. 34(A) to
(C).
[0165] Specifically, for example, in the case where the control
table illustrated in FIG. 34(A) is used, operation control of the
boost circuit 33A is performed so that the setting value of the
reference voltage Vref increases as the setting value of the output
voltage Vout (FC voltage, load voltage) increases. Thereby, the
constant voltage operation and the constant current operation
according to the setting value of the FC voltage are able to be
performed.
[0166] In addition, for example, in the case where the control
table illustrated in FIG. 34(B) is used, when the supply amount of
the liquid fuel 41 from the fuel pump 42 is constant, the
magnitudes of the output voltage Vout (FC voltage, load voltage)
and the output current lout (FC current, load current) are adjusted
according to the size of the load 6. Thereby, in a state in which
the fuel supply amount per unit time is constant, FC voltage and FC
current settings according to the load condition are able to be
performed.
[0167] In addition, for example, in the case where the control
table illustrated in FIG. 34(C) is used, operation control of the
boost circuit 33A is performed so that the output current lout (FC
current, load current) decreases as the setting value of fuel
conversion efficiency in the power generation section 10 increases.
Thereby, when the constant voltage operation is performed, the fuel
supply amount and the fuel conversion efficiency are able to be
optimized.
[0168] Thus, in this embodiment, the power generation voltage V1
(input voltage Vin) supplied from the power generation section 10
is increased by the boost circuit 33A and supplied to the load (the
secondary battery 34 and the load 6) as the output voltage Vout
(load voltage). At this time, the operation of the boost circuit
33A is controlled using a given control table, and therefore the
output voltage Vout (load voltage) and the output current lout
(load current) supplied from the boost circuit 33A to the load is
controlled.
[0169] Further, in this embodiment, as described hereafter, it is
more preferable to use the constant voltage control than the
constant current control.
[0170] First, a relation between generated power and the constant
voltage operation or the constant current operation will be
described with reference to FIG. 35.
[0171] First, in the constant current operation illustrated in FIG.
35(A), as indicated by a referential symbol P11 in the figure, even
if the fuel supply amount (cc/h) per unit time is increased, output
power (FC power) does not increase with the fuel increase and is
almost constant.
[0172] Meanwhile, in the constant voltage operation illustrated in
FIG. 35(B), as indicated by an arrow P12 in the figure, the output
power (FC power) is able to be increased by increasing the fuel
supply amount (cc/h) per unit time. It is also clear that the width
(voltage range) of the FC voltage .DELTA.V1 capable of obtaining
maximum power is of a certain size. In result, by generating power
in a state in which the FC voltage is a constant value, power
generation is able to be performed in a state in which a
proportional relationship is established between the FC power and
the fuel supply amount.
[0173] Next, a relation between fuel conversion efficiency and the
constant voltage operation or the constant current operation will
be described with reference to FIG. 36.
[0174] First, in the constant current operation illustrated in FIG.
36(A), as indicated by an arrow P13 in the figure, the fuel
conversion efficiency is at the highest when the fuel supply is
performed at a rate of 0.302(cc/h) (when the fuel supply amount is
the smallest in the figure). However, the current value width
.DELTA.I2 when the fuel conversion efficiency is at the highest
value is narrow and, further, the fuel conversion efficiency
suddenly deteriorates when the current value width .DELTA.I2 is
exceeded.
[0175] Meanwhile, in the constant voltage operation illustrated in
FIG. 36(B), the voltage value width .DELTA.V2 when the fuel
conversion efficiency is at the highest value is wide. In this case
as well, as indicated by an arrow P14 in the figure, the fuel
conversion efficiency is at the highest when the fuel supply is
performed at a rate of 0.302(cc/h) (when the fuel supply amount is
the smallest in the figure). In addition, as described above, since
the FC power is able to be changed according to the fuel supply
amount per unit time, by performing power generation in a state in
which the FC voltage is a constant value, power generation in a
state in which the proportional relation is established between the
FC power and the fuel supply amount, and power generation in a
state in which fuel conversion efficiency is high become possible
at the same time.
[0176] Thereby, in the case where operation control of the boost
circuit 33A is performed so that the output voltage Vout (load
voltage, FC voltage) becomes constant (where control is performed
to perform constant voltage operation), the power generation state
of the fuel cell 1 in particular is able to be made favorable.
[0177] Thus, in this embodiment, the power generation voltage V1
(input voltage Vin) supplied from the power generation section 10
is increased by the boost circuit 33A and the operation of the
boost circuit 33A is controlled using a given control table in the
control section 35A, and therefore control is performed on the
output voltage Vout (load voltage) and the output current lout
(load current) supplied from the boost circuit 33A to the load (the
secondary battery 34 and the load 6). Thus, even in the case where
intermittent fuel supply is performed in the vaporization supply
type fuel cell 1, efficient control of the output voltage Vout and
the output current lout is actualized. In result, power generation
that is more stable than in the past is able to be performed in the
vaporization supply type fuel cell.
[0178] In addition, in the case where operation control of the
boost circuit 33A is performed so that the output voltage Vout
(load voltage) becomes constant (where control is performed to
perform constant voltage operation), the power generation state of
the fuel cell 1 in particular is able to be made favorable.
[0179] In the foregoing first and second embodiments and the
variation example thereof, the description has been given of the
case that control is performed so that the temperature of the power
generation section 10 becomes constant (PID control is performed)
by proportioning the supply amount of the liquid fuel with the time
integral and the time derivative of the difference value between
the target temperature Tsv(s) and the detected temperature Tpv(s).
However, for example, control may be performed so that the
temperature of the power generation section 10 becomes constant
using other feedback control, such as P control and PI control,
fuzzy control, H.infin. control, and the like. Specifically,
control may be performed so that the temperature of the power
generation section 10 becomes constant (P control is performed) by
proportioning the supply amount of the liquid fuel with the
difference value between the target temperature Tsv(s) and the
detected temperature Tpv(s). Further, control may be performed so
that the temperature of the power generation section 10 becomes
constant (PI control is performed) by proportioning the supply
amount of the liquid fuel with the time integral of the difference
value between the target temperature Tsv(s) and the detected
temperature Tpv(s). In addition, control may be performed so that
the temperature of the power generation section 10 becomes constant
(PD control is performed) by proportioning the supply amount of the
liquid fuel with the time derivative of the difference value
between the target temperature Tsv(s) and the detected temperature
Tpv(s).
[0180] In addition, in the foregoing first and second embodiments
and the variation example thereof, the description has been given
of the case that the heat generation correction section 352
calculates the energy conversion efficiency .eta. in the power
generation section 10 using the power generation voltage (detected
voltage) V1 detected by the voltage detection section 32. However,
the energy conversion efficiency .eta. in the power generation
section 10 may be calculated using a previously set given voltage
(setting voltage) instead of such a power generation voltage
V1.
[0181] Further, the circuit structures of the boost circuit 33A and
the voltage division circuit 37 are not limited to those described
according to the foregoing third embodiment, and may be circuit
structures using other methods. In addition, the control table is
not limited to those described according to the foregoing third
embodiment (FIGS. 34(A) to (C)), and a control table having other
structures may be used.
[0182] Further, in the foregoing embodiments and the like, the
description has been given of the case that the power generation
section 10 includes the six unit cells that are electrically
connected to each other in series. However, the number of unit
cells is not limited thereto. For example, the power generation
section 10 may be composed of one unit cell, or may be composed of
two or more given plurality of unit cells.
[0183] Further, in the foregoing embodiments and the like, air
supply to the oxygen electrode 13 is performed by natural
ventilation. However, air may be forcefully supplied by using a
pump or the like. In this case, oxygen or gas containing oxygen may
be supplied instead of air.
[0184] Further, in the foregoing embodiments and the like, the
description has been given of the case that the fuel tank 40
containing the liquid fuel 41 is built in the fuel cell systems 5
and 5A. However, such a fuel tank may be detachable from the fuel
cell system.
[0185] Further, in the foregoing embodiments and the like, the
description has been given of the direct methanol fuel cell system
but can be also applied to other type of fuel cell systems.
[0186] The fuel cell system of the present embodiments is able to
be suitably used for a mobile electronic device such as a mobile
phone, an electronic camera, an electronic databook, and a PDA
(Personal Digital Assistants).
[0187] It should be understood that various changes and
modifications to the presently preferred embodiments described
herein will be apparent to those skilled in the art. Such changes
and modifications can be made without departing from the spirit and
scope of the present invention and without diminishing its intended
advantages. It is therefore intended that such changes and
modifications be covered by the appended claims.
* * * * *